A. Field of the Invention
The present invention relates to the fields of molecular biology, biochemistry, and oncology. More particularly, the invention provides for the inhibition of p53 transcription by interfering with the activity of a p53 promoter using inhibitory double-stranded RNAs.
B. Related Art
p53 was identified some two decades ago as a tumor suppressor, and its mutation is implicated in at least 50% of all cancers. Though it has been the focus of intense research, new information continues to emerge about its complex biology. For example, it is now known that p53 is a member of a structurally-related family including p63 and p73, each of which expresses multiple RNA species with dozens of theoretic isoforms. p53 produces multiple mRNA alternative splice forms using at least four different promoters, one of which lies within intron #4, just upstream of exon 5. And though p53's normal role is in the inhibition of the cancer phenotype, the presence of dominant negative mutations in p53 can impede the normal apoptotic pathway that wild-type p53 induces, thereby resulting in resistance of certain cancers to other forms of therapy, such as radio- and chemotherapeutics.
Rohaly et al. (2005) reported on a novel p53 isoform present in most cells that is produced by alternative splicing of exons 7 through 9, designated as Δp53. This isoform transactivates the endogenous p21 and 14-3-3a promoters, but not the mdm2, bax or PIG3 promoters, and does so only in damaged S phase cells. Upon activation of the ATR-intra-S phase checkpoint, Δp53, but not p53, transactivates p21, resulting in downregulation of cyclin A-Cdk activity and attenuation of S phase progression. This results in uncoupling of repair and replication events. Interestingly, the region of Δp53 that is deleted is one where a large number of mutations occur, including those resulting in dominant negative mutants of p53. This region, identified as 257-323 of the wild-type sequence, lies at the C-terminal region of the DNA binding domain, and abuts the N-terminal region of the oligomerization domain. The ability of this isoform to function as a bona fide tumor suppressor gene remains to be determined.